The present invention relates to a top-seal wrapping device and a top-seal wrapping method. The present invention particularly relates to a top-seal wrapping device for covering an opening of a tray with a stretch film, welding the stretch film to a peripheral portion of the tray opening, and thermally cutting the stretch film. The present invention also relates to a top-seal wrapping method for performing such wrapping.
An over-wrapping method has been widely used for wrapping fresh foods, such as meat and fish, as well as processed foods such as precooked meals. In a conventional over-wrapping method, a tray is entirely wrapped with a film after arranging the intended contents or a wrapping target therein.
In the over-wrapping method, however, the tray and contents must be wrapped entirely, and the film portions must be overlapped with each other for sealing. Therefore, the film must have a size that is several times as large as the planar size of the tray. In many cases, the film portions overlap each other on the bottom of the tray, and the bottom surface of the tray is pressed against a heater plate for sealing. Therefore, the sealing ability or reliability is low.
However, a method, which will be referred to as a top-seal method, has been used instead of the over-wrap method in some cases. In the top-seal method, a film is arranged only over the opening at the top of the trap, and is welded to the peripheral portion of the tray around the opening. In this top-seal method, the required amount of film can be reduced when compared with the over-wrap method.
This top-seal method has been widely employed for wrapping mushrooms such shimeji mushrooms and others. More specifically, the top-seal method is implemented primarily in such a manner that adhesive is applied to a side surface of a tray around an opening, and ends of a film covering the opening are adhered thereto. Alternatively, the top-seal method is implemented in such a manner that a tray and a film having a larger area than the planar area of the tray are held between dies, and are welded together by pressure and heat applied thereto.
Between the above methods, the method of performing the welding with dies can hermetically seal the tray containing contents, i.e., a target to be wrapped, and therefore is superior to the over-wrap method. In the prior art, however, dedicated dies corresponding to tray forms and sizes are employed, and a hard film is used for the wrapping.
It may be envisaged to weld a stretch film (stretchable film) to the tray instead of a hard film. However, stretch film is liable to wrinkle, and when stretch film is placed over the tray the stretch file and contents may exhibit a less desirable appearance than when using the hard film. It is necessary to transport the stretch film, which is thin and does not have sufficient rigidity, to and from a position for welding. Therefore, a large and/or complicated mechanism may be required for the transportation.
An object of the present invention is to provide a wrapping device and a wrapping method for performing wrapping by welding a stretch film to a tray. Particularly, an object of the present invention is to provide a wrapping device and a wrapping method, which has a good appearance after the wrapping, and can employ a transporting mechanism with a compact structure.
According to a first aspect of the present invention, the present invention provides a top-seal wrapping device for covering a top opening of a tray containing a wrapping target with a stretch film, welding the stretch film to a peripheral portion of the tray around the opening, and thermally cutting the stretch film. The top-seal wrapping device includes a stretch mechanism, a control portion, and a film winding portion. The stretch mechanism stretches the stretch film. The control portion controls the stretching of the stretch film by operating the stretch mechanism at least before welding the stretch film to the tray. The film winding portion winds up the stretch film after the thermal cutting.
In the wrapping device of this aspect, the stretch film covers the opening of the tray, is welded to the peripheral portion of the tray around the opening, and is thermally cut.
The stretch film thus cut is wound up. Owing to the structure operating as described above, a transporting mechanism having a compact structure can be used for transporting a thin stretch film having low rigidity. In the prior art, the stretch film is transported by belts holding the opposite sides of the film, or by chains moving in the transporting direction and having clamps for holding the film. This requires a large and/or complicated structure, and increases costs. In contrast to this, the wrapping device of this aspect is provided with a film winding portion for ensuring the continuity of the stretch film. Therefore, a stretch film, which is thin and does not have sufficient rigidity, can be transported without holding or pinching it. Accordingly, the transporting mechanism can have a compact structure.
Further, the stretch mechanism is arranged for stretching the stretch film at least before welding the stretch film to the tray. Therefore, wrinkles of the stretch film covering the opening of the tray are expanded before welding so that the appearance is improved in the wrapped state.
According to a second aspect of the present invention, the top-seal wrapping device of the first aspect further has a feature such that the stretch film is thermally cut at a position outside a portion welded to the peripheral portion around the tray opening.
According to a third aspect of the present invention, the top-seal wrapping device of the first or second aspect further has a feature such that the control portion operates the stretch mechanism to apply a tension to a portion of the stretch film near the cut portion at least after welding the stretch film.
In this structure, the tension is applied to the portion near the cut portion after thermally cutting the stretch film. Therefore, the cutting can be completed even when an uncut portion is left. Further, the tension may also be applied to the stretch film during the thermal cutting. This allows easier cutting of the stretch film.
Since the stretch film is stretched after the cutting, problems can be suppressed such as the remaining portion of the cut stretch film clinging to the tray or the like.
According to a fourth aspect of the present invention, the top-seal wrapping device of the first, second, or third aspect further includes a film transporting mechanism and a lift mechanism. The film transporting mechanism transports the stretch film. The lift mechanism lifts the tray to push the stretch film transported by the film transporting mechanism against the tray. The control portion operates the stretch mechanism to stretch the stretch film before contact of the tray with the stretch film, and also controls the stretch mechanism to reduce tension of the stretch film after the contact of the tray with the stretch film.
In this structure, the lift mechanism pushes the tray against the stretch film to achieve a state in which the stretch film covers the opening of the tray.
Further, the stretch film is stretched before the tray comes into contact with the stretch film. Therefore, no wrinkles are present in the stretch film when it comes into contact with the tray, and the opening of the tray is covered with the stretch film without a wrinkle.
Further, tension of the stretch film is reduced after the tray comes into contact with the stretch film. Therefore, a disadvantage in which the stretch film is excessively stretched due to relative movement between the stretch film and the tray caused by the lift mechanism after contact between the stretch film and the tray can be suppressed.
According to a fifth aspect of the present invention, the top-seal wrapping device of any one of the preceding aspects further has a feature such that the stretch mechanism is arranged between a supply position of the stretch film and an end of a position of the welding.
According to a sixth aspect of the present invention, the top-seal wrapping device of any one of the preceding aspects further includes a detecting means. The detecting means detects an opening in the stretch film formed by thermal cutting. The control portion controls the stretch mechanism not to act on at least a portion of the stretch film including and neighboring the opening detected by the detecting means.
In this structure, the opening in the stretch film formed by the thermal cutting is detected. The control is performed such that the stretching of the stretch film may not be effected on the portion including and neighboring the detected opening. Thus, control is performed to stop the stretching of the stretch film having a portion, which was thermally cut and removed. Therefore, meandering and entangling of the stretch film are suppressed even if the strength and rigidity of the film are reduced due to the partial cutting.
According to a seventh aspect of the present invention, the top-seal wrapping device of any one of the preceding aspects further has a feature such that the stretch mechanism has a plurality of film holding portions for holding the stretch film.
In this structure, the plurality of film holding portions holds the stretch film. Therefore, the film holding portion can be arranged at (or moved to) the positions corresponding to the configuration of the tray for appropriately stretching the stretch film in accordance with the tray configuration.
According to an eighth aspect of the present invention, the top-seal wrapping device of the seventh aspect further has a feature such that the plurality of film holding portions can be set to have different holding forces, respectively.
According to a ninth aspect of the present invention, the top-seal wrapping device of the seventh or eighth aspect further has a feature such that the control portion changes timing of holding and releasing operations of the plurality of film holding portions based on the properties of at least one of the tray and the stretch film.
In this structure, the stretch film can be stretched in accordance with the properties of the tray such as a tray configuration and/or the properties of the stretch film such as a material of the stretch film.
According to a tenth aspect of the present invention, the top-seal wrapping device of any one of the preceding aspects further has a feature such that the stretch mechanism stretches the stretch film in at least one of either the transporting direction of the stretch film or the width direction perpendicular to said transporting direction.
According to an eleventh aspect of the present invention, the present invention provides a top-seal wrapping method for covering a top opening of a tray containing a wrapping target with a stretch film, welding the stretch film to a peripheral portion of the tray around the opening, and thermally cutting the stretch film. The top-seal wrapping method includes a film supply step, a stretch step, and a film winding step. In the film supply step, the stretch film is transported to a position above the tray. In the stretch step, the stretch film is stretched in a direction crossing the transporting direction before welding the stretch film to the tray. In the film winding step, the stretch film is wound after the thermal cutting.
According to a twelfth aspect of the present invention, the top-seal wrapping device of the first aspect further includes a film supply mechanism, a lift mechanism, a heating body, and a tray holding member. The film supply mechanism supplies the stretch film to a position above the tray. The lift mechanism lifts the tray to push the tray against the stretch film. The heating body comes into contact with the peripheral portion of the tray surrounding the opening and contacts the stretch film for welding the stretch film to the peripheral portion of the tray around the opening. The tray holding portion holds the tray when welding the stretch film to the peripheral portion of the tray around the opening.
A conventional top-seal method has been employed for wrapping mushrooms such as shimeji mushrooms and others. More specifically, the top-seal method is implemented primarily in such a manner that adhesive is applied to side surfaces of a tray around an opening. Ends of the film covering the opening are adhered thereto, or in such a manner that the tray and the film having a larger area than the planar area of the tray are held between dies. The tray and the film are welded together by pressure and heat applied thereto.
However, the conventional top-seal method described above requires dies corresponding to the forms and sizes of trays. Therefore, the over-wrap method has been widely employed rather than the top-seal method in the fields, which use various types of trays because contents must be arranged in various types of trays having different sizes and/or forms. Although the top-seal method can reduce the required amount of film and can improve the sealing performance, it is necessary in the prior art to prepare dies for each of the trays having different forms and/or sizes. Therefore, the top-seal method has not been employed in some or many cases.
For overcoming the above disadvantage of the top-seal method in the prior art, the assignee has proposed in Japanese Patent Application No. 1999-137025 a device for performing heat sealing (thermal welding) in a manner such that a heating roller is brought into contact with a peripheral portion of a tray around an opening with a film therebetween. The heating roller is pivoted around an axis for welding the film. According to this device, sealing can be effected without a problem if the trays have sizes and forms falling within appropriate ranges. In conventional devices, different dies are required for different types of trays. In the device proposed by the assignee, however, tooling change is not particularly required if the trays have sizes and forms falling within certain ranges. Thus the sealing operation can continue without a tooling change.
The assignee has also proposed, in Japanese Patent Application No. 1999-154616, a device for performing heat sealing in a manner such that a tray covered with a stretch film is pushed against a rubber sheet heated by a heater. In this device, it is not necessary to prepare dies dedicated to each of the trays of different forms and sizes, and the sealing operation can continue without tooling change even after a change to a different type of tray.
In the devices proposed in Japanese Patent Publication Nos. 1999-137025 and 1999-154616, however, the tray receives a force from the heating roller or the rubber sheet in the heat sealing operation. This force may shift a planar position of the tray so that large differences may occur in sealing pressure between various portions of a flange of the tray during the heat sealing operation. In the heat sealing operation, it is desired that the heating roller or the rubber sheet is pushed to various portions of the tray flange with uniform pressure A sealing failure may occur locally if the center of the tray shifts from the pivoting center of the heating roller or the center of the rubber sheet.
Accordingly, the top-seal wrapping device of the twelfth aspect of the present invention employs a structure for pushing the tray against the stretch film supplied to a position above the tray. Also, the heating body is brought into contact with the peripheral portion of the tray surrounding the opening and pushed against the stretch film so that the stretch film is welded to the tray. Further, the tray holding member is employed for holding the tray so that the position of the tray may not shift or deviate due to contact with the heating body when welding the stretch film to the tray. Therefore, the tray can maintain an optimum position with respect to the heating body, and the heating body can come into contact with the peripheral portion of the tray around the opening in accordance with the designed manner. This can reduce sealing failures due to positional deviation of the tray.
Positional deviation of the tray may occur linearly on a plane, angularly on a plane, and/or in a direction of the height. The tray holding member is configured in accordance with the characteristics of the device, and can hold the tray to prevent positional deviation in at least one of the above directions.
The tray holding member may be configured to be in direct contact with the tray for holding the tray, or may be configured to hold indirectly the tray by appropriate means such as suction.
According to a thirteenth aspect of the present invention, the top-seal wrapping device of the twelfth aspect further has a feature such that the tray holding member prevents shifting of the position of the tray when the tray is lifted and pushed against the stretch film.
In this structure, the tray holding member holds the tray to prevent positional deviation of the tray not only when welding the stretch film to the peripheral portion of the tray around the opening but also when the tray rises and comes into contact with the stretch film. Therefore, it is possible to prevent positional deviation of the tray due to the contact with the stretch film. Thus, sealing failure can be suppressed more effectively.
According to a fourteenth aspect of the present invention, the top-seal wrapping device of the twelfth or thirteenth aspect further has a feature such that the tray holding member comes into contact with a side surface of the tray to prevent shifting of the planar position of the tray.
According to a fifteenth aspect of the present invention, the top-seal wrapping device of the twelfth, thirteenth, or fourteenth aspect further includes a tray carrying and holding mechanism. The tray carrying and holding mechanism is configured to carry the tray thereon and to be transported to the lift mechanism together with the tray. The tray holding member is included in the tray carrying and holding mechanism. The lift mechanism lifts the tray by lifting the tray carrying and holding mechanism.
In this structure, the tray is placed on the tray carrying and holding mechanism to prevent positional deviation of the tray by the tray holding mechanism. While maintaining this state, the tray is transported to the lift mechanism by transporting the tray carrying and holding mechanism to the lift mechanism. Then, the lift mechanism lifts the tray carrying and holding mechanism to move the tray upward. Therefore, positional deviation of the tray can be prevented during transportation to the lift mechanism as well as lifting by the lift mechanism. Accordingly, the sealing (welding) by the heating body is effected on the tray located in the designed position so that the sealing can be performed more stably.
According to a sixteenth aspect of the present invention, the top-seal wrapping device of any one of the twelfth to fifteenth aspects further has a feature such that the tray carrying and holding mechanism is configured to bias the tray holding member toward the tray to adjust the planar position of the tray.
In this structure, the tray carrying and holding mechanism serves not only to prevent positional deviation of the tray by the tray holding member but also to adjust the planar position of the tray (e.g., to center the tray). When adjusting the planar position of the tray, the tray holding member is biased toward the tray. For example, a spring, an electric motor, a pneumatic cylinder, or a hydraulic cylinder may be used for biasing the tray holding member toward the tray.
As described above, the tray holding member adjusts the position of the tray, and holds the tray while preventing positional deviation of the tray. Thereby, operations such as transfer of the tray from a position adjusting portion to a holding portion are not required, thus, the structure can be simple.
According to a seventeenth aspect of the present invention, the top-seal wrapping device of any one of the twelfth to fourteenth aspects further includes position detecting means. The position detecting means detects the positional state of the tray during transportation to the lift mechanism. The control portion corrects position shift of the tray by the tray holding member based on a result of the detection by the position detecting means.
In this structure, the tray holding member corrects positional deviation of the tray, and the tray holding member also holds the tray to prevent positional deviation of the tray. In this manner, the tray holding member is used for correcting positional deviation and preventing subsequent positional deviation, thus, the device can have a simple structure.
According to an eighteenth aspect of the present invention, the top-seal wrapping device of any one of the twelfth to fourteenth aspects further includes biasing means. The biasing means biases the tray holding member toward the tray. The control portion controls a biasing force of the biasing means.
In the above structure, the tray holding member is biased toward the tray for holding the tray, and thereby prevents positional deviation of the tray. Further, to allow adjustment of the tray holding force, the control portion is configured to control the biasing force of the biasing means. Therefore, the force for holding the tray can be changed depending on parameters such as hardness and the material of the tray. For example, the holding force can be controlled to be low for soft trays, and to be high for hard trays. Thereby it is possible to suppress sealing failure due to deformation of the tray while reliably preventing positional deviation of the tray.
According to a nineteenth aspect of the present invention, the top-seal wrapping device of the eighteenth aspect further includes biasing force detecting means. The biasing force detecting means detects the biasing force applied by the biasing means. The control portion controls the biasing force of the biasing means based on a result of the detection by the biasing force detecting means.
In the aforementioned structure, since the biasing force detecting means is employed, the biasing means can be controlled while determining the actual biasing force, i.e., actual tray holding force. Therefore, a situation in which an excessively large biasing force collapses a soft tray does not occur. Further, the tray can be held with a holding force that corresponds to the properties of the tray.
According to a twentieth aspect of the present invention, the wrapping device of the eighteenth aspect further has a feature such that the control portion controls the biasing force of the biasing means corresponding to the properties of at least the tray and/or the stretch film.
In this structure, the biasing force of the biasing means, and thus the holding force for the tray can be adjusted in accordance with the properties of the tray such as hardness and material of the tray, and/or the properties of the stretch film such as thickness and material of the stretch film.
According to a twenty-first aspect of the present invention, the top-seal wrapping device of the first aspect further includes a film supply mechanism, a lift mechanism, a heating body, and a position adjusting mechanism. The film supply mechanism supplies the stretch film to a position above the tray. The lift mechanism lifts and pushes the tray against the stretch film. The heating body comes into contact with the peripheral portion of the tray surrounding the opening and being in contact with the stretch film. The heating body welds the stretch film to a peripheral portion of the tray around the opening. The position adjusting mechanism adjusts the planar position of the tray before the tray comes into contact with the stretch film.
According to the device of the above aspect, the tray is pushed against the stretch film supplied to a position above the tray. Additionally, the heating body is brought into contact with the peripheral portion of the tray, which is located around the opening and is in contact with the stretch film, for welding the stretch film to the tray. Further, the tray is located at an optimum position for the heating body when welding the tray to the stretch film, and for this purpose, the position adjusting mechanism is employed for adjusting the planar position of the tray before pushing the tray against the stretch film. Therefore, the tray located at the adjusted optimum position comes into contact with the stretch film, and is welded by the heating body to the stretch film. In this structure, as described above, the position of the tray with respect to the heating body is adjusted to be optimal so that sealing failures due to positional deviation of the tray can be suppressed.
According to a twenty-second aspect of the present invention, the top-seal wrapping method of the eleventh aspect further includes a position adjusting step, a lift step, and a welding step. The position adjusting step is executed by adjusting the planar position of the tray. The lift step is executed by lifting and pushing the tray against the stretch film. The welding step is executed by bringing a heating body into contact with the peripheral portion of the tray located around the opening and being in contact with the stretch film, and thereby welding the stretch film to the peripheral portion of the tray around the opening.